1. Field of the Invention
The present invention relates to an automotive bumper and its manufacturing process.
2. Description of Prior Art
An automotive bumper is the piece attached to the front and rear of a car to serve as an energy dissipation device in a collision, thereby protecting the auto body and the driver. Particularly in the case of a passenger car, the aesthetic requirement of the bumper, which appears on the outside of the vehicle, is stressed in addition to the above collision-energy management requirement.
Conventional automotive bumpers can be breadly classified into:
1) Energy absorbing types such as:
(a) a stable-type consisting of a steel bumper plus a shock absorber (Menasco type), or PA1 (b) a polyurethane bumper, or PA1 (c) a non-stable type consisting of a bumper made entirely of fiber reinforced plastics (FRP) which can absorb the energy of destruction itself.
2) Hybrid composite bumpers having a metal shell and a plastic backing, such as a foam backing or a FRP backing, or
3) Ordinary types such as a steel bumper securely fastened to the auto chassis.
The last mentioned commonly-used steel bumper has drawbacks in that it is heavy, thereby increasing the vehicle inertia. Moreover, since it is fitted at the front and rear ends of a vehicle, it is unfavorable for controlling longitudinal vibrations of a vehicle, i.e., so-called pitching. By contrast, the polyurethane bumper is light and can restore itself after a collision, but it cannot be given a metallic luster and it is thus limited in design versatility. Meanwhile, the bumper made entirely of FRP, which is usually metallic-coated or metallized for aesthetic reasons, defies a treatment to give it a durable, metallic luster.
The hybrid composite bumper having a metal shell and plastic backing previously lacked sufficient adhesion between the metal shell and plastic backing to allow acceptable joining of these elements at their interface. Good adhesion between the two elements provides a pleasant feel of structural integrity, thereby enhancing the commercial value of the bumper and contributing to its rigidity as well as reducing its weight. Thus, good adhesion has been one of the important requirements in a bumper of this kind.
This problem of adhesion has been addressed in three U.S. Pat. Nos. 4,545,105, 4,569,865 and 4,339,144, which disclose methods for bonding a metal member to a foamed or fiber reinforced plastic backing so as to provide an automotive bumper consisting of a firmly integrated structure of metal and plastic. Such bumpers now exhibit metallic luster and good appearance and also are considerably lighter than their solid steel counterparts.
None of these patents teach plating of the outer surface of the metal shell to further enhance the appearance of the bumper, before or after attachment of the plastic backing. Chrome plating the metal shell prior to affixing the plastic backing would not be advisable due to damage to the plating during the insertion and removal of the metal shell from the mold used to bond the shell to the backing. Additionally, removal of any resin or foam that has flowed around the edges of the metal shell during the molding process would probably be done by mechanical or chemical methods which would further damage any chrome plating.
Furthermore, it would not be economically desirable to invest the cost of chrome plating in a metal shell, prior to its being bonded to a plastic backing, if the entire bumper assembly were subsequently discarded due to inadequate bonding between the metal shell and the backing.
A method and apparatus thereby need be developed that takes advantage of the light weight of a hybrid composite bumper, wherein the process of fabrication allows plating of the outer surface of the metal shell.